1. Field of the Invention
The present invention is related to a knife track adjustment structure of thread cutter of a sewing machine. A front guide board of a swing arm is up and down adjustably displaceable on the base board, whereby the position of a thread cutter composed of a knife arm and a hook rod arm can be drivingly adjusted so as to rectify the movement track of the thread cutter. A spring is compressed between the swing arm and the base board to help in restoring the thread cutter.
2. Description of the Prior Arts
U.S. Pat. No. 6,234,097 discloses a thread cutter of sewing machine. The thread cutter includes a fixed plate 1, a knife arm 2, a hook rod arm 3, a cantilever assembly 4 and cooperative conventional securing member 63, cutting knife 64, hook rod 66 and swing arm 67. The periphery of the fixed plate 1 is formed with locating holes for mounting the fixed plate 1 on the sewing machine. The fixed plate 1 is formed with a mounting recess 12 in which one end of the knife arm 2 is placed. The other end of the knife arm 2 is formed with perforations 23 and thread holes 24 for mounting the securing member 63 and the cutting knife 64. The hook rod arm 3 is formed with left and right slots 31, 32 and a notch 33. One end of the swing arm 67 is placed in the notch 33 for driving the hook rod arm 3 to displace. The tail end of the hook rod arm 3 is assembled with the hook rod 66. In cooperation with the securing member 63 and the cutting knife 64, the thread cutter can perform thread cutting operation.
The thread cutter is characterized in that the cantilever assembly 14 is composed of a left and a right cantilevers 41, 42 and fixed with the fixed plate 1. The left cantilever 42 has a downward directed projecting post 423 placed in the left slot 32 of the hook rod arm 3. The projecting post 413 of the right cantilever 41 is inserted in the perforation 26 of the lug 25 of the knife arm 2. The projecting post 413 serves as a fulcrum about which the knife arm 2 swings so as to greatly reduce the swinging torque of the hook rod arm 3 and knife arm 2. The tail end of the knife arm 2 is formed with a slot 22. The projecting post 35 under the tail end of the hook rod arm 3 is placed in the slot 22, whereby the hook rod arm 3 can more stably operate to enhance the quality of the thread cutting operation.
However, the above thread cutter structure has some shortcomings as follows:
1. The left cantilever 42 is substantially N-shaped. One leg of the left cantilever 42 is locked on the fixed plate 1, while the other leg is cantilevered. The bottom end of the cantilevered leg has a projecting post 423 placed in the left slot 32 of the hook rod arm 3. When the hook rod arm 3 or the knife arm 2 slides, due to rubbing, the cantilevered leg of the left cantilever 42 often co-vibrates. This makes it impossible for the hook rod arm 3 or knife arm 2 to operate in a smooth move track or even a noise is produced.
2. When the swing arm 67 restores the knife arm 2 and hook rod arm 3, due to the gap between the respective components, such as the gap between the swing arm 67 and the notch 33 of the hook rod arm 3, the knife arm 2 and the hook rod arm 3 often cannot be accurately restored. This results in inaccurate thread cutting operation.
3. The bending section 321 of the left slot 32 of the hook rod arm 3 is continuously rubbed by the projecting post 423 of the left cantilever 42 and is widened. This leads to enlarged gap between the projecting post 423 and the bending section 321. Accordingly, the thread cutting operation can be hardly accurately performed.
4. The projecting post 413 of the left cantilever 42 placed in the left slot 32 of the hook rod arm 3 is spaced from the fixing point where the left cantilever 42 is fixed on the fixed plate 1. That is, a force arm exists. When the hook rod arm 3 reciprocally slides, the bending section 321 of the left slot 32 will collide the projecting post 413. The action force multiplies the force arm to produce a bending torque onto the fixing point where the left cantilever 42 is fixed on the fixed plate 1. As a result, the left cantilever 42 is very easy to loosen and detach.
In addition, U.S. Pat. Nos. 5,469,798, 5,481,994, 5,870,962, 5,887,535, 6,021,727, 6,205,941 and 6,378,448 disclose other thread cutter structures.
It is therefore a primary object of the present invention to provide a knife track adjustment structure of thread cutter of sewing machine. By means of up and down adjusting the guide seat or the swing arm on the lower shaft inner cover, the positions of the thread cutter composed of the fixed knife seat and movable knife seat can be drivingly adjusted so as to rectify the movement track of the thread cutter.
It is a further object of the present invention to provide the above knife track adjustment structure of thread cutter of sewing machine in which the guide seat is a straight plate and upper and lower ends of the guide seat are firmly fixed on the lower shaft inner cover. When the thread cutter operates, the guide seat will not vibrate or co-vibrate as the conventional cantilever structure. Therefore, the movement track is smoothened and no noise or vibration will be produced.
It is still a further object of the present invention to provide the above knife track adjustment structure of thread cutter of sewing machine in which a spring is mounted between the lower shaft inner cover and the swing arm to restore the thread cutter to predetermined position so as to avoid inaccurate thread cutting operation.
According to the above objects, the thread cutter of sewing machine of the present invention includes a lower shaft inner cover over which a fixed knife seat is bridged. A movable knife seat is bridged over the fixed knife seat. The movable knife seat is driven by a driving arm to stably axially slide on the fixed knife seat. The knife track adjustment structure includes: a guide seat bridged over the lower shaft inner cover, an upper and a lower ends of the guide seat being locked on the lower shaft inner cover, the guide seat being up and down adjustably displaceable on the lower shaft inner cover, whereby the fixed knife seat and a middle section of the movable knife seat bridged over the fixed knife seat are permitted to slide between the guide seat and the lower shaft inner cover, a guide spacer ring being disposed under the middle section of the guide seat, the guide spacer ring being sequentially passed through a first guide slot of the movable knife seat and a guide slot of the fixed knife seat; and a swing arm, a first end of the swing arm being pivotally connected with the lower shaft inner cover, a spacer ring being disposed under the bottom of the second end of the swing arm, the spacer ring being sequentially passed through a second guide slot of the movable knife seat and pivotally connected on the fixed knife seat, a spring being compressed between the swing arm and the lower shaft inner cover to help in restoring the fixed knife seat and movable knife seat.